EIGHT whales stranded off the northern tip of New Zealand’s South Island will be euthanised after attempts over two day to refloat them proved unsuccessful.

The pilot whales that originally stranded on Farewell Spit on Tuesday were refloated on Wednesday and volunteers helped stop them beaching again when they were forced out of the water at nightfall.

The whales were found beached again on Thursday morning.

Department of Conservation ranger John Mason says they will not attempt to rescue them again and they will be euthanised on Thursday morning.

“It’s been 48 hours since they stranded now, and they’ve been refloated twice, and they have had every chance to move to deeper water,” he told AAP.

“They are now starting to show signs of physical deterioration and they are noticeably agitated, more than before.”

The original group which stranded on Tuesday was made up of 13 whales, but five had died by Wednesday morning.

The remaining eight were refloated at high tide on Wednesday by DOC staff, Project Jonah volunteers and members of the local community, and a boat was used to keep them from stranding again during the day, but they did not show any signs of going back to sea.

Windy conditions on Thursday morning meant a boat could not be used if another attempt was made to refloat them, Mr Mason said.

Pilot whales regularly become stranded on Farewell Spit and last Monday 39 were stranded there. All either died or were euthanised.